One of the main problems during the extraction and transport of crude oil is the foam formation, due to the presence of gas. In general, the greater tendency to foam formation and collapse occurs in crude oils with densities lower than 40 API degrees. Foaming, substantially, causes operational problems such as: low productivity, pump cavitation (Fallin et al, 1971), deposits formation, liquid drag into gas streams, gas and water drag into streams of crude oil and reduction in separator capacity (Wylde et al, 2008). Depending on the nature of the crude oil and the type of separators used, the foaming problems (drag of liquids into gas streams and gas entry in liquid streams) can reduce the crude oil production and even cause shutdowns of the process. The problems result in a flooding of equipment and containers, which can also cause reductions in the capacity of the gas-crude oil separators. (Poindexter et al, 2002).
A defoamer is a chemical product with surfactant properties and, when it is present in a dissolution, facilitates the foam removal. It must be insoluble in the crude oil, to provoke sudden gradients into the crude oil-gas surface tension, not be sensitive to temperature changes and be resistant against chemical compounds and oxidation attacks (Prud'homme R. et al., 1996). The crude oil or petroleum is a mixture of hydrocarbon compounds, gases and liquids. Generally, the crude oil is in liquid phase and it can also contain small amounts of sulfur, nitrogen and oxygen compounds and metal traces, (Speight J., 2001).
The inhibition of foam formation in crude oils is a multifactorial complex problem. The literature on the subject reports that an efficient antifoaming agent needs to penetrate the gas/oil and to spread over the surface of the oil (Blute et al, 1994). Among the commercial products used as defoamers for crude oils, it can be mentioned the following: silicones and fluorosilicones, phosphate esters, metal surfactants of fatty acids, sulfonated compounds, amides, polyglycols, glycol esters, polyethers, fatty acid esters and alcohols (Prod'homme et al, 1996). Among those ones, the most used are silicon-based products because of their high antifoaming ability, since these chemicals are effective at low concentrations around 10 ppm or less. However, silicon-based defoamers in massive use present problems such as catalyst poisoning in refining processes, as well as the formation of deposits in other subsequent stages.
Traditionally, silicone (dimethylpolysiloxane) was used for foam inhibition treatment. In U.S. Pat. No. 2,702,793 a mixture of dimethylsilicone and amyltriethoxysilane is employed for inhibiting foam formation in crude oils. Similarly, in U.S. Pat. No. 2,862,885 is described the use of a monovinylalkoxysilane defoamer in crude oil. In the other hand, U.S. Pat. No. 4,005,044 discloses the use of a dimethylpolysiloxane liquid as antifoaming agent in a solution of emulsifying agent.
In order to improve the performance of polysiloxanes as defoamers, some chemical modifications have been made to these polymers. A chemical modification is to obtain copolymers such as linear copolymer of fluoro-alkyl polysiloxane, as is indicated by the U.S. Pat. No. 4,329,528, with a composition between 20 to 70 mol % of fluorosilicone, presenting a great performance at high temperatures (in the range from 25 to 370° C.) and good solubility in crude oil. This copolymer is used in the crude oil reserves as a method to inhibit or suppress foaming, adding at least 1 ppm of this antifoaming agent (Evans, 1982).
International Patent WO 97/38067 and U.S. Pat. No. 6,001,140A application describe the use of copolymers, which have a structure consisting of polysiloxane and over which one is grafted an organic group, particularly a polymer with MDxD′yD″zM formula, where M is O0.5Si(CH3)3, D is OSi(CH3)2, D′ is OSi(CH3)R and D″ represents OSi(CH3)R′. At the same time, R is a polyhydric organic group C6-C28, while R′ is a phenol derivative or an aliphatic long chain group.
Cassani F. et al. presented studies at laboratory and field level in the evaluation of six commercial silicon-based antifoaming agents in crude oils with medium density (21 to 27° API), as well as optimal dosages to control foam generated in separation equipment. Optimal dosages in a range from 0.01 to 1 ppm were found for these silicon-based antifoaming agents (formulation containing between 2 to 4 wt % of silicon in kerosene as a solvent) in a medium crude oil with 26.3° API at laboratory level. These dosages were also corroborated at field level.
Due to operational drawbacks involving silicon-based products, for some time new alternatives without silicon compounds have been sought, to evaluate them as antifoaming agents in crude oil. Such antifoaming agents called “silicon-free” are organic compounds consisting essentially of sulphates and phosphates (Hart, 1992), vegetal (Hart, 1994) and animal oils (Hart, 1995), polyisobutylene compounds (Hart, 1995 and Hart, 1998), polypropylene oxide/polyethylene oxide block copolymers (Hart, 1998) and mixtures of the previous ones.
Vegetal oils such as jojoba oil (Simmondsia chinensis) and animal oils such as mink oil (Neovison vison) have been used to control foam at high temperatures (150 to 500° C.) in hydrocarbon fluids during distillation and/or delayed coking processes of crude oil, as it is shown in U.S. Pat. No. 5,296,132A and U.S. Pat. No. 5,389,299A, respectively. Effective dosages as antifoaming agents in the patents cited were in the range from 10 to 1000 ppm (Hart, 1994 and 1995) and because of the low viscosity of these products, they may be added in pure form or in solution.
U.S. Pat. No. 5,472,637A and U.S. Pat. No. 5,800,738A describe the use of high molar mass polyisobutylene (between 2000 and 2 000 000 Da) and low molar mass polyisobutylene (320 Da), being efficient as defoamers in crude oil and/or derivatives of it.
In addition, alkylphenolformaldehyde alkoxylated compounds with block copolymers of propylene oxide/ethylene oxide have been developed, with molar masses between 2000 to 6000 Daltons, for foaming control in hydrocarbon hydrocracking separation systems in dosages from 15 to 1500 ppm as it is indicated in U.S. Pat. No. 5,750,052A.
In drilling or well treatments, some methods have been developed to prevent the formation or break down of foam, where the treated fluid is a liquid which is added with an antifoaming agent. According to the antifoaming agent composition this may be useful in well conditioning (drilling fluids, foundation fluids, etc.). This addition prevents foaming and air drag during stirring, mixing or pumping of those fluids. The composition of these antifoaming agents comprises a carboxylic acid amide, a propylene glycol, and a fatty alcohol (C12-15) ethoxylated and propoxylated (Chatterji, 2007, 2009, 2011).
Rezende D. A., et al. assessed the efficiency of commercial block copolymer poly (ethylene oxide)-poly (propylene oxide) and polysiloxanes grafted polyethers antifoaming agents in two crude oil samples with similar SARA compositions (saturated, aromatics, resins and asphaltenes analysis), as well as its density and viscosity, (Danielle, 2011). Polysiloxanes grafted with polyethers like pendant groups showed the best performance as foam inhibitors in the crude oils.
Wylde J. has studied the formation of foam in crude oil from northern Alberta, Canada, with densities from 10 to 12° API. However, using the assessment method for foam formation described in his study (modification from standard ASTM D892-13 method) and due to the high viscosity of super-heavy crude oil selected to be evaluated (12° API), it was not feasible to create relevant foam levels to perform the evaluations of the antifoaming agents in study. To overcome this difficulty, a considerable amount of n-heptane was added to super-heavy crude oil, in order to create an artificial light crude oil with lower viscosity and to thus measure the foam inhibitory efficiency of the antifoaming agents. Obviously, the addition of n-heptane provokes asphaltenes loss in the crude oil. The antifoaming agents studied were all silicon-free chemicals: compounds based on sulfates and phosphates, ethoxylated esters, polyethylene-glycol esters, ethoxylated alcohols (11 commercial chemicals obtained from market). In these field assessments mixtures of sulfonated salts and ethoxylated fatty alcohol adducts with ethylene oxide and propylene oxide showed to be effective as defoamers. One limitation of this study is that the mentioned chemicals are only effective as defoamers in deasphalted crude oil and not in real heavy crude oils.
As regards on polyacrylates or acrylic compounds, there are several references to their application in the conditioning of petroleum and its derivatives. Its capacity has been reported as antifoaming agents in oil derivatives from petroleum, such as: lubricating oils for internal combustion engines, pumps lubricant oils, hydraulic oils, etc. These lubricants may be synthetic or natural, as described in U.S. Pat. No. 3,166,508. The major efficiency of polyacrylates as antifoaming agents in petroleum derivative lubricating oils is observed at concentrations from 10 to 50 ppm. However, the polyacrylates disclosed in this patent have the disadvantage of being effective only in certain types of oil. The patent to which it is referenced do not make mention of the application of polyacrylates as antifoaming agents in crude oil conditioning process. This patent does not disclose adjusting the molecular weight of the polyacrylates in order to increase their efficiency as antifoaming agents in specific samples of crude oil. U.S. Pat. No. 5,766,513 describes the combination of a fluorosilicone-based antifoaming agent with one defoamer based on polyacrylate which is effective to reduce the foam in lubricant oils at low and high temperatures. However, by themselves, none is efficient in reducing foam at same assessment conditions. In the other hand, it has been reported that copolymers based on acrylates and terpolymers based on alkyl methacrylate monomers, wherein the alkyl moiety contains a fluoroaliphatic group of 3 to 20 carbon atoms, have shown to increase the resistance to foaming once they are added to hydrocarbon lubricant oils. The copolymers and terpolymers based on acrylates are disclosed in U.S. Pat. No. 7,700,527 and EP 1029030, respectively.
Among other applications of the polyacrylates for petroleum conditioning, different to the foam formation inhibition, their use as pour point depressor in crude oils with high content in paraffinic waxes as disclosed in U.S. Pat. No. 3,951,929. Acrylics also have shown high performance as viscosity reducers in heavy crude oils, such as described in U.S. Patent Publication 2011/0067295 (Castro, 2011). Previously, it has been shown than alkyl acrylates homopolymers (polymers which contain only a single type of repeat unit) exhibited a good performance as antifoaming agents in gasified heavy and super heavy crude oil (Patent Publication MX/a/2013/014352).